Treatment Of Hexavalent Chromium Pollution By Biochar And Its Modified Materials

With the rapid development of industrialization in modern society,the heavy metal Cr（Ⅵ）has been widely used in the process of industrial production.The discharged Cr（Ⅵ）pollutants are highly toxic and accumulate in the environment for a long time,which also causes great harm to the natural environment that people rely on for survival.In particular,the problem of Cr（Ⅵ）pollution in soil and groundwater is becoming increasingly prominent.As a low-cost and stable remediation material,biochar has been gradually applied to the treatment of heavy metal pollution in water and soil due to its good effect on the remediation of heavy metals.Based on this,this paper used corn cob and industrial waste as raw materials to prepare biochar at different temperatures,and selected 500℃industrial waste and 300℃corn cob biochar with better adsorption effect for alkali modification treatment.To study the adsorption effect of industrial wastes and corncob biochar on Cr（Ⅵ）before and after modification under different adsorption conditions,analyze the role played by industrial wastes and corncob biochar in the adsorption process of Cr（Ⅵ）,and clarify the leading adsorption mechanism in the adsorption process.Then,the passivation effect of industrial wastes and corn cob biochar on Cr（Ⅵ）contaminated soil was further studied through soil culture experiments.Finally,a PRB permeable reaction wall was established with GC300 as the reaction medium,and the removal effect of PRB on Cr（Ⅵ）in groundwater was investigated.This study provides reference for the selection and practice of Cr（Ⅵ）restoration materials in actual restoration engineering.Results indicate that:（1）When p H=2,initial concentration of Cr（Ⅵ）is 40 mol·L^-1,and the amount of adsorbent is 40 mg,it is more conducive to the adsorption of Cr（Ⅵ）by I500,GI500,C300and GC300 biochar.（2）The adsorption process of corn cob and industrial waste biochar on hexavalent chromium pollutants before and after alkali modification is more suitable to the quasi secondary kinetic model,which indicates that the process is chemical adsorption,which mainly depends on the complexation of surface functional groups;the adsorption of Cr（Ⅵ）on biochar belongs to monolayer adsorption,which is more consistent with the Langmuir isothermal model.（3）The surface pore structure of corncob and industrial waste biochar is developed,and the fiber structure is extremely uneven.On the biochar surface,there are much-OH,-NH,C=O,-COOH and C-O.The surface of biochar modified by alkali has more flaky structure,obvious surface wrinkles,and more-OH and-NH are introduced.The BET specific surface area and total pore volume of GC300 and GI500 biochar were larger than those of C300 and I500.After adsorption of Cr（Ⅵ）,the specific surface area of biochar decreased significantly,the vibration of characteristic peaks such as-OH,-COOH decreased,and the typical characteristic peaks corresponding to cr-o bond appeared,which indicated that the surface of biochar was complexed by functional groups.（4）Corn cob and industrial waste biochar materials can effectively fix Cr（Ⅵ）in soil,and the residual Cr（Ⅵ）concentration(3.887～4.724mg·kg^-1)in soil after treatment is lower than the screening value of Cr（Ⅵ）pollution risk(5.7mg·kg^-1)in the second type of construction land.（5）When the concentration of Cr（Ⅵ）was 10 mg·L^-1and the flow rate of solution was lower than 0.12 ml·min^-1,the removal rate of Cr（Ⅵ）by alkali modified corncob biochar was89.02%.Comprehensive study shows that alkali modified industrial waste and corncob biochar have good adsorption effect on Cr（Ⅵ）,which has a certain application prospect for remediation of Cr（Ⅵ）contaminated soil and groundwater.